Breakage of plant stems, trunks (e.g., saplings), and/or stalks (collectively referred to as “stems”) due to bending can drastically reduce crop yields. For example, maize stalk lodging (breakage of the plant stalk during wind and rain storms) reduces yields of by about 5% annually (Duvick, 2005). Such failures also prevent the development of higher yielding plant varieties because large and heavy grains and kernels cause premature stalk breakage. Increasing the bending strength of plant stems is therefore important to both current production and future development.
In plants, bending strength is affected by both genetic and environmental factors. Environmental pressures such as water availability, temperature, and soil composition can have strong effects on plants' strength. Structural failure is often caused by severe weather events. All of these factors make it difficult to distinguish between genetic and environmental effects on strength, even when collecting data across multiple years and across varied environments. An accurate method to quantify the bending strength of plants would enable improvements through selective breeding and genetic modification.
Various mechanical tests have been developed to measure stalk strength. Crush tests were developed and applied to excised maize stalk segments (Thompson, 1964; Zuber and Grogan, 1961) to select stronger stalks. Rind penetrometers have been used for recurrent selection and quantitative trait locus (QTL) mapping (Peiffer et al., 2013) of maize, and three-point bending has been used for QTL mapping and corn stalk characterization (Hu et al., 2013). Recent studies in other grass species have used similar approaches (Jin et al., 2009; Kokubo et al., 1991; Li et al., 2003; O'Dogherty et al., 1995).
Current methods of measuring stalk strength are labor-intensive and time consuming, making them unattractive to plant breeders. In general, prior art methods use indirect alternatives to predict or estimate strength. For example, geometric measurements such as diameter, chemical measurements such as lignin content or mechanical measurements such as force to pierce the stalk with a needle. Recent research has revealed that the predominant failure pattern (or failure modes) of maize stalks is a distinctive crease near the node (Robertson et al., 2015). Previous studies of stalk strength induce failure patterns that are substantially different, thus explaining their limited utility in addressing the problem of stalk lodging.
A tool which provides a, reliable, and quantitative measurement of stem strength, ideally replicating the type of breakage experienced in nature, would be very valuable to plant breeders as it would enable selective breeding for increased strength and reduced lodging propensity.